WPF would probably be that. In any case, modern UI toolkits often are vector-based anyway because of UI scaling. Heck, even ancient ones are, if you look at the

WPF would probably be that. In any case, modern UI toolkits often are vector-based anyway because of UI scaling. Heck, even ancient ones are, if you look at the Marlett font. That contained scalable UI elements for Windows 95.